# How to reproduce
- Install the l10n_th module
- Use the demo TH company
- Ensure you have the demo invoices and credit notes associated to that company
- Go to the Tax Report
- Select Tax Report (TH)
- Click on "Sales Tax Report (xlsx)"

# The problem
The Credit Notes' Total Amount, Total Excl and Vat Amount are positives. They should be negative instead. The same issue appear for "Purchase Tax Report (xlsx)".
This issue also concerns Credit Notes created manually in the Journal Entries

# Why
The logic for the sign of the value fields in the reports is the following :

```py
sign = move.reversed_entry_id.payment_state == 'partial' and -1 or 1
```

This is unreliable because a Credit Note will not always have a reversed_entry_id associated or if it has one, it's payment_state may change

A refactor of theses reports has been made for versions 19.0+ but it seems too big to backport (https://github.com/odoo/enterprise/pull/75645/changes)

Instead, we just check if the current move's type is a refund. If yes, we reverse the sign.

opw-6006720

**Problem:**
When a customer's language is changed and an invoice is reprinted, all invoice fields translate correctly except for product names and descriptions, which remain in the original language.

**Steps to reproduce:**
1. Create an invoice for a customer with English language
2. Post the invoice (product names appear in English)
3. Change the customer's language to French
4. Reprint/download the invoice PDF
5. Observe that product names still appear in English instead of French

**Current behavior:**
Product names remain in the original language when reprinting invoices after changing the customer's language.

**Expected behavior:**
Product names and descriptions should dynamically translate based on the customer's current language setting when the invoice is reprinted.

**Cause of the issue:**
The invoice report template uses `line.name`, which is a stored text field frozen at invoice creation time. This field contains the product name in whatever language was active when the line was created and does not update when the partner's language changes. When rendering the PDF, this frozen text is displayed regardless of the current language context.

**Fix:**
Use `product_id.display_name` instead of `line.name` for product-linked invoice lines. The `display_name` field is computed dynamically and respects the current language context during PDF generation. For lines without a product (manual entries, notes, sections), fall back to `line.name` to preserve existing behavior. This allows product names to translate on reprint while maintaining compatibility with non-product lines.

opw-5887170

### Issue before this commit:
When creating an invoice using the child contact of a parent contact that has a different language with respect to the father, the label of the invoice line was not always displayed in the child contact language but in the father's contact language.

### Steps to reproduce the issue:
1. Activate at least 2 languages (X and Y)
2. Create a product and set the translation for that product in the activated languages
3. Create a Contact with the language X
4. Create a child contact (invoice adress type) for that contact with language Y
5. Create a new invoice setting the customer as the child contact
6. Add the product you created
7. See the label is displayed in the language of the parent contact

### Cause of the issue:
The computation of the invoice line name relied on line.partner_id.lang. However, the partner_id of the move line is automatically set to the commercial partner that can be different (can be the father's contact) to the contact used on the invoice. As a result, the product description was translated using the wrong language.

### Reason to introduce the fix:
To ensure that invoice line labels are correctly translated according to the language of the selected invoice contact, the computation now uses the language of move_id.partner_id instead of line.partner_id. This guarantees consistent and expected behavior in multilingual environments, especially when using different contacts under the same commercial partner.

opw-5955875

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